1. Field of the Invention
This invention is concerned with a production of at least one thermal head having ridge-shaped glaze structure. More specifically, the invention is concerned with the production of a thermal head substrate that divides into a plurality of thermal heads after forming a plurality of ridge-shaped glaze layers adjacent to and in parallel with one another over a principal surface of the substrate.
2. Description of the Prior Art
Conventionally a thermal head is produced as follows.
First, a glass paste is printed in a pattern having adjacent bands in parallel over the principal surface of a substrate by a screen printing method.
Next, it is treated by heating to form ridge-shaped glaze layer having an arcuate section.
Then, a plurality of isolated individual resistors are formed by patterning after electrically resistive material is deposited in the vicinity of the ridge-shaped glaze layer.
Finally, a plurality of isolated individual traces are formed by patterning after electrically conductive material is deposited on the substrate. Each of traces connects at one end to each of the resistors and applies heat to the resisters.
Conventionally ceramics are utilized as the substrate. The substrate portions formed without the glaze layer have porous surfaces with a roughness of about 1 .mu.m so that they are liable to cause defects such as shorted or broken traces. Due to a slight difference in the wettability between the principal surface of the substrate and the glass paste, moreover, the width of the glaze layers may vary or their surfaces may undulate, thus creating the potential of another defect in that the adjacent glaze layer may merge into each other.